1. I'll find it myself when the time comes to replace my TV, thanks

Don't need to kill my afternoon reading HT threads today.
2. I think $700 is expensive. I know there are $2000 sound bars, but those are super niche. I think the top-selling sound bar on Amazon is the Vizio one. It also has a kit that comes with a wireless sub and two satellites wired to the sub. Depending on size, kit, and particular sale, it ranged from $250-$400. It has better-than-most HT-in-a-box quality. I would consider that mid-range for a sound bar. There are of course cheapo ones for under $100. Given those data points, I think it's fair to expect a lot from a $700 one.
I'm not trying to talk you out of the Playbar - if it works for you that's awesome. I would feel odd recommending something that costs $700 and doesn't have HDMI support is all.
Also, I agree that the Sonos zone thing is a huge benefit. If it had HDMI, I would buy it today no further questions asked.
3. When said TV upgrade comes, I will revisit Sonos. If it still has no HDMI, I'm going with the Bose probably. Or I might go down the full-blown AVR path, because I hate myself.
4. Looking back, it is confusing. But it's hard to do with text. If I could draw a picture, I think it actually looks less complicated than the non-ARC setup. It's that one two-way HDMI-ARC connection that is really difficult to diagram with words alone.